Microlithography processes for making miniaturized electronic components, such as in the fabrication of computer chips and integrated circuits, are of increasing importance as the trend towards miniaturization and integration continues. Lithography is one of the key technologies that drives the growth of the integrated circuit industry. Other important semiconductor processes include etch processes and implantation processes. These processes are building tools for fabricating integrated circuit chips.
Lithography processes, etch processes and implantation processes involve the use of masks. Masks contain patterns of translucent/transmissive areas and opaque/blocking areas. Masks function by selectively preventing or blocking a substance, such as light, electron beams, ions, etchants, etc., from portions of a subject substrate while permitting the substance to contact other portions of the subject substrate. In these semiconductor mask processes, improved masks and improved mask processing are desired since they would lead to improved products.
Lithography masks are employed to selectively irradiate a resist covered semiconductor substrate. Etch masks are used to selectively remove exposed areas of an underlying substrate. Ion implantation masks are used to selectively implant ions in exposed areas of an underlying substrate. Such masks are a critical aspect of semiconductor processing and lithographic processing in particular because they play an important role in achieving ever decreasing pattern specifications. Important factors associated with making and using masks include pattern position accuracy, feature size control, and defect density. Masks, whether they are lithography masks or etch masks or ion implantation masks, are made in compliance with a desired design rule (the design rule is derived from numerous aspects of the process).
Prior to using product masks in semiconductor processing (hereinafter termed using a "product mask"), a so-called "test mask" is fabricated to confirm and optimize the operability of a prospective mask design and technology, such as the relationships between patterning, etching, implants, and the like. In other words, test masks permit one to evaluate the technology (such as the acceptability of patterning, etching, and the like) of a prospective mask design. One concern associated with making and using masks, whether the mask is a product mask or a test mask, is that fabrication is complex and costly. Referring to FIG. 1, a conventional test mask 10 is shown. A conventional test mask 10 has test patterns 12 over a substrate. The test patterns 12 define various slits or openings 14 in the mask. The test mask 10 is used to determine whether or not the test patterns 12 lead to the production of desired patterned structures (in the case of a lithography test mask).
Another concern regarding masks is that a product mask derived from a corresponding test mask behaves in a different manner. These differences deleteriously impact subsequent semiconductor processing. For example, differences between a product mask and a corresponding test mask may lead to undesirable changes in resist images. During the image-wise irradiation, dense fields may change the amount of light (intensity) passing through the mask. During development, unanticipated concentrations of development components in localized areas affect the size and shape (such as sidewall slope) of openings. This is especially troublesome as resists having a poor slope undesirably permit implants to reach the underlying substrate.
Generally speaking, a lithography product mask that provides a patterned resist which does not accurately reflect the pattern formed by the test mask requires additional engineering and study in order to further refine/compensate the product mask, otherwise the electrical characteristics of semiconductor devices made therewith are unreliable. Such refinement undesirably consumes time and money. It is therefore desirable to provide product masks that act in the same manner as their corresponding test masks.